Uniting synthetic resin and metal



P 1934- E. c. LOETSCHER 1,972,307

UNITING SYNTHETIC RESIN AND METAL Filed Feb. 2, 1932 Patented sq. 4,1934 UNITED STATES PATENT oF -uca.

The primary object of this invention is to secure a satisfactory bondbetween a metal base and bakelite or bakelized material, therebyovercoming the persistent tendency toward blistering and separation ofthe bakelite or bakelized material from the metal due apparently to thegreat difference in the co-eflicient of expansion between the layers.

A further object of the invention is to produce a perfectly fiat, smoothsurface on the bakelite or bakelized material, which has heretofore beenfound diflicult when preparing products of relatively large surfaceareas, owing to the variations in the thickness of the metal used andthe variations in the accuracy of the presses employed.

With these and other objects in view, as will be pointed out as thedescription progresses, reference will be had to the accompanyingdrawing forming a part of this specification and wherein,

Fig. 1 is a diagrammatical view of the disposition of parts in making aproduct covered on one side only, and,

Fig. 2 is a similar view with respect to,a product covered on bothsides.

In the drawing, reference numeral 1 designates a metal base plate, ironand aluminum being specific examples, and this plate is first roughened,preferably by sandblasting, the blast being desirably directed at asharp angle to the metal base to give the added advantage ofundercutting to the roughen ng, whereby the adhesive applied to themetal base will find a better opportunity of securing a permanent holdupon the same. Sandblasting is followed by pickling or etching, thisbeing practised by subjecting the roughened metal base to a bath of 540%concentrated hydrochloric acid to 90-95% of water. These two steps leavethe metal base with a roughened and perfectly clean surface.

Reference numeral 2 represents a sheet of kraft or other paper,desirably unsized, which is treated, preferably by impregnation, with asynthetic resin of the phenol formaldehyde carbohydrate type such as isset forth in an application, filed February 11, 1931 and bearing SerialNumber 515,144. After impregnation, the water solvent in which thissynthetic resin is dissolved is only partially dried out so that some ofthe solvent remains for a purpose to be later elaborated.

Instead of impregnating the kraft paper 2 with the phenol formaldehydecarbohydrate resin, the sheet 2 may be first treated with bakelite byimmersion, impregnation, or by incorporating the same at the time ofmanufacture of the paper, and then coating the bakelized paper 2 withthe phenol formaldehyde carbohydrate resin, and as before, onlypartially drying out the water solvent therefrom.

The sheets 33 of paper treated with phenolic condensation products suchas bakelite, are juxtaposed upon the layer 2, and upon these layers ofbakelized paper 33, is then placed a layer 4 of fibrous material such aspaper or textile material, wood veneer or the like, either decorated orplain. The material of layer 4 is treated with phenolic condensationproducts, such as bakelite, preferably by impregnation in a solutionthereof diluted to the extent of approximately 50% with an alcoholsolvent. When wood veneer is employed for the layer 4, its thickness ispreferably 1/100" and impregnation is preferably conducted underhydrostatic pressure, but when materials such as paper or textiles areused for this layer 4, its porosity or capillary qualities" makesimpregnation by mere immersion satisfactory. In fact, treatment of anyof the layers employed herein may even be by brush coating, thoughcomplete saturation rather than mere surface coating of the layers isproductive of a more completely satisfactory product.

A layer 5, of tissue paper, cellophane, or the like, preferablyimpregnated, when possible, with bakelite or other phenolic condensationproduct may then be applied to the layer 4 to provide a transparentprotective covering therefor, but the use of this layer 5 is optional.

When the pack of layers 1, 2, 3--3, 4, 5, has been made up, it is readyfor the press. The pressure plates 6 and 8 are respectively placedagainst the top and bottom of the pack and a compound layer made up of alayer or layers 9 of felt attached to a sheet of rubber 10 is applied tothe bottom of the pressure plate 8, and the entire pack, including theplates and layers 6, 8, 9, 10 is inserted between the upper and lowerplatens 7 and 11 of a hydraulic press. These platens are equipped withusual provision for steam heating and water cooling. The lower face ofthe pressure plate 6 is highly polished to aid in preventing the samefrom becoming bonded with the product. The lower pressure plate 8 whichis against the metal plate 1 need not be polished.

The press is then operated to force the platens 7 and 11 toward eachother and to compact the pack. Steam is circulated through the upperplaten '7, the lower platen 11 remaining cool to avoid overheating-therubber to a degree that will destroy it or its elastic qualities. Thefelt layer 9 prevents the heat from the upper platen 7 being transmittedthrough the pack to the rubber layer 10 to similarly destroy thequalities thereof.

It is impossible to obtain paper, wood, metal or other sheets of.uniform thickness, or to produce a press of the kind used herein withoutinaccuracies, and because of these and other inaccuracies, it isimpossible to make products with such relatively large surface areas as12" x 12" without producing low pressure areas on the work, which resultin dull spots in which the bakelite was not able to flow sufficiently tomake a smooth and uniformly bright or polished surface film. A variationas low as .001 in the thickness of the pressure plates 6 and 8 andinequalities as low as .005" in the thickness of the press platens, arein themselves (not to mention the inaccuracies in the thickness of thelayers forming the product), sufficient to cause certain areas toreceive more pressure than others. Since the pressure plates 6 and 8cannot, when directly against the platens 7 and 11, bend to take up thevarious inequalities, a uniform surface can only be obtained in theproduct by employing a compressible layer such as the rubber 10. Anycompressiblematerial, such as fibre board, felted or textile materialcould be substituted for the rubber, but, because, these do notre-expand to their original thickness and soon lose all elasticity, theymust be discarded, where as rubber in retaining its elasticity may beused over and over again so long as it is protected from destructivedegrees of heat, for which protection the felt layer 9 is principallyprovided and only the upper platen 7 heated. During compression of thepack, the rubber layer 10 will compress in certain of its portions,becoming accommodated to the inaccuracies of the platens '1 and 11, ofthe pressure plates 6 and 8, and of the various layers of the product,thereby uniformly forcing the outer layer of the pack against thepressure plate 6 and eliminating the occurrence of dull surface spots. 1

When both sides of the metal plate 1 are to be covered, the variouslayers are prepared as before and reading top to bottom the layersconstituting the product are juxtaposed in the following order; 5, 4,33, 2, 1, 2, 3-3, 4, and 5. The pack thus constituted is then placedbetween the upper and lower platens 7 and 11 with the pressure plates 6and 8 intervening between them and the pack respectively, and thecompound sheet comprising the felt and rubber sheets 9 and 10respectively, with the rubber next to the platen 11, is then placedbetween the pressure plate 8 and platen 11. The platens are closed uponthe pack and, as before, steam is circulated through the upper platen 7only and the applied heat transmitted through the entire pack to reactthe synthetic resins. The platen 11 is not heated by the application ofsteam, and remains cool as a protection to the rubber againstvulcanizating the rubber 10. i

In both cases, after the synthetic resins have become reacted, the steamis cut ofi from the upper platen and water circulated therethrough tocool the product, after which the latter is removed for use.

Particular stress is placed upon the important part played by the phenolformaldehyde carbohydrate synthetic resin incorporated in layer 2 inobtaining a satisfactory bond between the bakelite or bakelized layersand the metal plate. Recognized authorities have expressed theirinability to obtain a satisfactory bond between large surfaces of metaland bakelite or bakelized material. This they ascribe to the greaterthermal expansion of the metal over the bakelite or bakelized materialwhich results in the bakelite or bakelized layer separating from themetal as soon as the product is removed from the press. That is, thebakelite or bakelized layer which has been consolidated with heat andpressure, separates from the metal plate. On the other hand, applicanthas discovered that his phenol formaldehyde carbohydrate synthetic resinnot only clings tenaciously to the metal base plate, but also forms aninseparable bond with bakelite or bakelite coated or impregnatedmaterial. Like bakelite, it reacts under heat and pressure, and, beingsimilar in many other respects to bakelite, forms a perfect bondtherewith due either to mutual adhesion or combination, or both.

Bakelite, or the same in bakelized material, in small surfaces where thedifferences in the coefficient of expansion thereof and metal areslight, may show some tendency to adhere to a metal base, though notwith the tenacity of applicants synthetic resin, but in large areaswhere the difference in expansion between these layers is material,bakelite will separate of its own accord from metal and when it does notnaturally separate therefrom it can be easily peeled off by means of aknife or finger nail. The synthetic resin, employed by applicant,however, will not separate because of the extreme changes of temperaturewhile in the press or because of any temperature changes encountered bythe product in ordinary use, and clings so tenaciously to the roughenedmetal that it cannot be peeled off at all even with a knife. In fact, inattempting to remove applicants coating or covering from the metal, thesame. must be scratched off and in instances actually dug out of theindentations in the metal plate.

Roughening of the metal plate is not an essential to the success of thisinvention, since tenacious bonds have been made with metal sheets havingthe finish imparted to them by the rolling mill, which in the case ofaluminum is quite lustrous. Satisfactory bonds for many purposes havebeen obtained with even very highly polished metal, but as with alladhesives the tenacity of bond decreases with the degree of polishpresent on the surface of the metal. It is pointed out, however, thatwhether polished or roughened, no satisfactory bond can be obtained atall between bakelite material and metal when the bakelite is dependedupon to produce the bond,

whereas with applicants phenol formaldehyde carbohydrate synthetic resininterposed, a bond with polished as well as rough metals can be obtainedthat prevents separation of the parts without destruction of one or bothof them.

The adhesive tenacity of the phenol formaldehyde carbohydrate syntheticresin is a natural characteristic thereof and requires no explanationbut why its bond with the metal base is not broken as in the case ofbakelite, due to the differencein the coefficient of expansion betweenthe metal plate and the superimposed bakelite or bakelized material,finds its most probable explanation in that this resin has the propertyof not reacting into an absolutely rigid state as bakelite and ofretaining a considerable degree of elasticity or plasticity due toretained moisture after reaction, which elasticity or plasticity isimparted to the entire layer 2. Hence the carbohydrate synthetic resinintervenes as a buffer between the metal and the rigid reacted bakeliteyielding, to compensate for the difference of coeflicient of expansionbetween the metal and bakelite or bakelized material.

In a test, an aluminum sheet preparedand covered as in the example ofFig. 1, was placed in a cold storage room with a temperature of 10 belowzero prevailing and maintained therein for a considerable period of timeand no separation of the bakelite or bakelized material from the metaloccurred. A similar test piece was then subjected to a temperature of220 F. for several days and as in the previous test no separationoccurred. The latter test, extending over a period sufllciently long toordinarily dry off any solvent which may be remaining in the material,would seem to establish the fact that the. water is incorporated in thematerial in the form of combined water in sufiicient quantity to imparta considerable degree of elasticity to the carbohydrate synthetic resinor material impregnated therewith. The recited tests were under extremesof temperature under which a bakelite bond with metal, at least inproducts of considerable area, would show separation immediately uponremoval thereof from the press, and applicant's bond in persistingthroughout these extremes of temperature is capable of persistingthroughout all the degrees of temperature that may be encountered inordinary use of his product. Some of these uses being in theconstruction of furniture, building and car trim, and the like. 1

Applicant has been unable to separate the bakelized layers from themetal base of his products mechanically by any peeling operation orwithout actual destruction or disintegration. of the attached layercontaining the carbohydrate synthetic resin.

While a number of layers have been specified as being present betweenthe outer finishing layer 4 (the layer 5 being protective and optionaliand the metal base 1, thenumber of' intervening layers may be variedsince these may be considered padding layers employed principally tocompensate for irregularities in the work- These layers, beingimpregnated with phenolic condensation product become more or lessplastic during reaction of thecondensation product permitting the outersurfaces of the outer layers to adjust themselves perfectly to contourof the platens or pressure plates, and incidentally it is within theprovince of thk; invention to give the pressure plates moldingconfigurations.

While the padding layers 2, 3-3 go a considerable ways toward producinga uniform surface, it is impossible without the use of the rubber layer10 or a layer of other compressible elastic material to obtain a uniformsurface finish in the product where large areas are involved because ofthe inaccuracies of the press platen and of the components of theproductitself.

What is'claimed is:

1. The method of making a laminated body, 7 consisting in interposingbetween a metal plate and a body of phenolic condensation product of thebakelite type or a body impregnated with such condensation product alayer of water soluble phenol formaldehyde carbohydrate condensationproduct or a layer of material impregnated therewith, drying out fromthe phenol formaldehyde carbohydrate condensation product some of thewater solvent but leaving a suflicient amount of solvent water thereinto finally become incorporated in the phenol formaldehyde carbohydratecondensation product as combined water to prevent the lattercondensation product from becoming as brittle and rigid after reactionas the phenolic condensation product, and reacting both condensationproducts under heat and pressure.

2. The method of making a laminated body, consisting intreating a simpleor compound layer to cause the same to present a phenolic condensationproduct of the bakelite type on its exposed and concealed faces,juxtaposing the same to a layer of metal, interposing a layer treated topresent on its opposite faces a water soluble phenol formaldehydecarbohydrate condensation product from which the water solvent no hasbeen only partially dried out, the remaining water finally becomingincorporated in the phenol formaldehyde carbohydrate condensationprodnot as combined water, and finally reacting both ble condensationproduct from which the water solvent has been only partially dried out,and reacting both condensation products under heat and pressure. 5

EMJL C. LOE'ISCHER.

